A chemical reaction can be activated or promoted either by the addition of energy to the reaction medium in the form of thermal and electromagnetic energy or by means of transferring energy through a physical catalyst. None of these methods are energy efficient and can produce either unwanted by-products, decomposition of the necessary transition state, or insufficient quantities of preferred products.
It is generally true that chemical reactions occur as a result of collisions between reacting molecules. In terms of the collision theory of chemical kinetics it is expected that the rate of a reaction is directly proportional to the number of the molecular collisions per second, or to the frequency of molecular collisions:
rate number of collision/sec PA1 a) completely replacing a physical chemical catalyst; PA1 b) acting in unison with a physical chemical catalyst to increase the rate of reaction; PA1 c) reducing the rate of reaction by acting as a negative catalyst; or PA1 d) altering the path of a reaction for formation of a specific product. PA1 a) duplicating at least one frequency of a spectral pattern of a physical catalyst; and PA1 b) exposing the reaction system to at least one frequency of the spectral pattern of the physical catalyst. PA1 a) determining an electromagnetic spectral pattern of the physical catalyst; and PA1 b) duplicating at least one frequency of the electromagnetic spectral pattern of the physical catalyst with at least one electromagnetic energy emitter source; and PA1 c) exposing the chemical reaction system to the at least one frequency of the duplicated electromagnetic spectral pattern in a sufficient amount and duration to catalyze the chemical reaction. PA1 a) duplicating at least one frequency of a spectral pattern of the physical catalyst with at least one electromagnetic energy emitter source; PA1 b) irradiating the chemical reaction system with the at least one frequency of the duplicated electromagnetic spectral pattern having a frequency range from about radio frequency to about ultraviolet frequency for a sufficient duration to catalyze the chemical reaction; and PA1 c) introducing the physical catalyst into the reaction system. PA1 a) determining an electromagnetic spectral pattern for starting reactant in said chemical reaction system; PA1 b) determining an electromagnetic spectral pattern for end product in said chemical reaction system; PA1 c) calculating an additive electromagnetic spectral pattern from said reactant and product spectral pattern to determine a catalytic spectral pattern; PA1 d) generating at least one frequency of the catalytic spectral pattern; and PA1 e) irradiating the reaction system with at least one frequency of the catalytic spectral pattern.
This simple relationship explains the dependence of reaction rates on concentration. Additionally, with few exceptions, reaction rates increase with increasing temperature because of increased collisions.
The dependence of the rate constant k of a reaction can be expressed by the following equation, known as the Arrhenius equation: EQU k=Ae.sup.-Ka/RT
where Ea is the activation energy of the reaction which is the minimum amount of energy required to initiate a chemical reaction, R the gas constant, T the absolute temperature and e the base of the natural logarithm scale. The quantity A represents the collision frequency and shows that the rate constant is directly proportional to A and, therefore, to the collision frequency. Furthermore, because of the minus sign associated with the exponent E.sub.a /RT, the rate constant decreases with increasing activation energy and increases with increasing temperature.
Normally, only a small fraction of the colliding molecules, the fastest-moving ones, have enough kinetic energy to exceed the activation energy, therefore, the increase in the rate constant k can now be explained with the temperature increase. Since more high-energy molecules are present at a higher temperature, the rate of product formation is also greater at the higher temperature. But, with increased temperatures there are a number of problems which are introduced into the reaction system. With thermal excitation other competing processes, such as bond rupture may occur before the desired energy state can be reached. Also, there are a number of decomposition products which often produce fragments that are extremely reactive, but they are so short lived because of their thermodynamic instability that a preferred reaction may be dampened.
Radiant or light energy is another form of energy that may be added to the reaction medium without the negative side effects of thermal energy. Addition of radiant energy to a system produces electronically excited molecules that are capable of undergoing chemical reactions.
A molecule in which all the electrons are in stable orbitals is said to be in the ground electronic state. These orbitals may be either bonding or nonbonding. If a photon of the proper energy collides with the molecule, i.e., the photon is absorbed and one of the electrons may be promoted to an unoccupied orbital of higher energy. Electronic excitation results in spatial redistribution of the valance electrons with concomitant changes in internuclear configurations. Since chemical reactions are controlled to a great extent by these factors, an electronically excited molecule undergoes a chemical reaction that may be distinctly different from those of its ground-state counterpart.
The energy of a photon is defined in terms of its frequency or wavelength, EQU E=h.nu.=hc/.lambda.
where E is energy; h is Plank's constant, 6.6.times.10.sup.-34 J.sec; .nu. is the frequency of the radiation, sec.sup.-1 ; c is the speed of light; and .lambda. is the wavelength of the radiation. When a photon is absorbed, all of its energy is imparted to the absorbing species. The primary act following absorption depends on the wavelength of the incident light. Photochemistry studies photons whose energies lie in the ultraviolet region (100-4000 .ANG.) and in the visible region (4000-7000 .ANG.) of the electromagnetic spectrum. Such photons are primarily a cause of electronically excited molecules.
Since the molecules are imbued with electronic energy upon absorption of light, reactions occur from entirely different potential-energy surfaces from those encountered in thermally excited systems. However, there are several drawbacks of using the known techniques of photochemistry, that being, utilizing a broad band of frequencies thereby causing unwanted side reactions, undue experimentation, and poor quantum yield.
A catalyst is a substance which alters the reaction rate of a chemical reaction without appearing in the end product. It is known that some reactions can be speeded up or controlled by the presence of substances which themselves remain unchanged after the reaction has ended. By increasing the velocity of a desired reaction relative to unwanted reactions, the formation of a desired product can be maximized compared with unwanted by-products. Often only a trace of catalyst is necessary to accelerate the reaction. Also, it has been observed that some substances, which if added in trace amounts, can slow down the rate of a reaction. This looks like the reverse of catalysis, and, in fact, substances which slow down a reaction rate have been called negative catalysts. Known catalysts go through a cycle in which they are used and regenerated so that they can be used again and again. A catalyst operates by providing another path for the reaction which can have a higher reaction rate or slower rate than available in the absence of the catalyst. At the end of the reaction, because the catalyst can be recovered, it appears the catalyst is not involved in the reaction. But, the catalyst must take part in the reaction, or else the rate of the reaction would not change. The catalytic act may be represented by five essential steps:
1. Diffusion to the catalytic site (reactant) PA0 2. Bond formation at the catalytic site (reactant) PA0 3. Reaction of the catalyst-reactant complex PA0 4. Bond rupture at the catalytic site (product) PA0 5. Diffusion away from the catalytic site (product).
The exact mechanisms of catalytic actions are unknown but they can speed up a reaction that otherwise would take place too slowly to be practical.
There are a number of problems involved with known industrial catalysts: firstly, catalysts can not only lose their efficiency but also their selectivity, which can occur due to overheating or contamination of the catalyst; secondly, many catalysts include costly metals such as platinum or silver and have only a limited life span, some are difficult to rejuvenate, and the precious metals not easily reclaimed.
Accordingly, what is needed is a method to catalyze a chemical reaction without the drawbacks of known physical catalysts and with greater specificity than thermal and known electromagnetic radiation methods.